Investigate whether or not circulating tumor antigens can be used as a diagnostic tool by following levels of circulating antigens during tumor growth in a variety of situations and attempting to relate the measured levels of antigen to tumor size. The experiments shall be carried out with a wide range of rat tumors being transplanted into syngeneic recipients. These tumors are 3-methylcholanthrene-induced sarcomas, hepatocellular carcinomas and spontaneously arising mammary adenocarcinomas in Wistar rats.